Low-permittivity materials of trimethylsilane-based carbon-doped oxide (SiOC) for interconnect interlayers were synthesized by inductively coupled plasma (ICP) methods. Methyl groups and Si-O-Si cage structures in ICP SiOC films were explored as two dominant factors in determining the electrical and material characteristics of such films. The high ionization efficiency from ICP, resulting in SiOC films that contain low hydrogen (low defect sites) but high oxygen concentrations (enhanced porous densities), yields such films with a high breakdown field of 6.8 MV/cm, a low leakage current below 1.0 x 10(-10) A/cm(2) (at 1.0 MV/cm), and a dielectric constant below 2.9. (C) 2003 The Electrochemical Society.